Saccharomyces Boulardii

Supplements · Probiotics · Supplement, Typed Supps

A helpful yeast, not a bacteria — which is exactly why antibiotics don’t wipe it out.

Stage by stage

Intake (Capsule): Being a yeast, it naturally survives stomach acid better than many bacterial strains.
Stomach (Survives acid well): Passes through the acid barrier more reliably than bacterial probiotics.
Intestine (Temporary presence): Temporarily present in the gut.
Gut lining (Supports during upset): Studied specifically for supporting gut lining function during digestive upset.

What the evidence supports

Preventing antibiotic-associated diarrhoea — moderate evidence. Meta-analyses pooling 20-plus randomised trials show roughly a halving of relative risk (risk ratio around 0.47). Trials are heterogeneous and one large hospital trial in unselected patients was negative, so the effect is real but not uniform.
Shortening acute infectious diarrhoea, including in children — limited evidence. Several randomised trials suggest about a day shorter duration, but studies are mostly small, varied in setting, and of modest quality.
Preventing travellers' diarrhoea — limited evidence. Some supportive trial data but fewer and less consistent than the antibiotic-associated diarrhoea evidence.
Evidence that it causes Causing fungaemia (a bloodstream yeast infection) in critically ill, immunosuppressed, or central-venous-catheter patients — moderate evidence. Documented through dozens of case reports and formal regulatory review; European regulators now contraindicate it in these groups and several fatal cases have been recorded. The risk in healthy people is very low.

Typical dose

250-500 mg (roughly 5-10 billion CFU) once or twice daily; trials most often used 250 mg twice daily

Upper limit: No established upper limit by dose; the key safety boundary is the patient group (avoid in the immunosuppressed) rather than the number of milligrams

Timing

Often used during or after antibiotics, since antibiotics don’t affect this yeast the way they affect bacteria.

Time to effect

Days: Any reported digestive effect in studies.

Medication interactions

Systemic antifungal medication (e.g. fluconazole): Antifungals act against the yeast itself, so they can neutralise the probiotic taken at the same time. (moderate)

Common myth

“All probiotics get wiped out by antibiotics.” In reality: Because this is a yeast, not a bacteria, antibiotics don’t affect it — part of why it’s specifically used alongside them.